High power electric machines and other high power electric devices require robust power connections capable of reliably transferring high currents and insulating high voltages. In the case of fluid-sealed machines or devices, the connection also requires sealing against the machine or device enclosure to prevent fluid from entering or exiting the enclosure through any of the connection interfaces. In the case of internally fluid-cooled machines or devices, the connection requires sealing against the machine or device enclosure to prevent leakage of cooling fluids.
One traditional method used for making power connections to electric machines is to provide a threaded stud constructed of material with relatively high electrical conductivity, such as copper or brass, connected to the internal wiring of the machine. With this method, as illustrated in FIG. 1, the threaded stud 10 is inserted through an insulated block 11. The assembly is then inserted through the machine housing wall 17 and captured with an insulated washer 12 and locking nut 13. The power connection is completed by securing the power cable ring lug connector 14 with additional locking nuts 15, 16 which apply pressure against the other locking nut 13.
One drawback for this stud connection design is that the threaded stud 10 and locking nut 13 need to be constructed of material with relatively high electrical conductivity, especially when used in high current applications. However, materials with high electrical conductivity tend to also have low mechanical yield strength properties, making them prone to failure when threaded hardware is used to secure the electrical connection, and thus may not survive many assembly and disassembly cycles without damage.
Additionally, another drawback of a traditional stud connection design is that the electrical current must flow through the threads of the locking nut 13 to the threads of the stud 10 to complete the electrical circuit, providing only limited line contact and not much surface area contact. This is especially troublesome in high current applications, where the limited electrical contact may result in additional resistive losses that may lead to overheating of the connection.
Another traditional method for making power connections is the terminal connection or “flying lead” method. This method, as shown in FIG. 2, involves terminating the internal wiring of an electric machine 17 directly with a ring lug connector 18. The external power connection cable for the machine is also terminated with a ring lug connector 19. These ring lug terminations 18, 19 are then connected together with a threaded fastener 20 and nut 21, or with a threaded fastener 20 to a terminal strip acting as the nut. The threaded fastener 20 and nut 21 apply pressure between the contacting surfaces of the ring lug connectors 18, 19 to complete the electrical path.
This method allows for an improved electrical connection over the stud connection design, because pressure is applied between the two large surfaces of the ring lug connectors 18, 19. This produces an effective connection with low resistance and high current capacity.
However, with the terminal connection method, because the two sets of wires are directly connected external to the machine, a method is needed to seal the wires as they exit the machine through the machine housing or other enclosure wall in the case of a fluid-sealed machine. In this case, the entire connection may need to be accessible, yet may also need to be contained in some type of sealed enclosure, making this design approach undesirable where a compact form factor is important.
Thus, a need exists for a method of high power connection that may achieve a robust electrical and mechanical connection interface. A further need exists that may addresses the issue of sealing the connection for fluid-sealed and/or internally fluid-cooled machines or devices.